Reteachable switching circuit with ability for locking

ABSTRACT

A method for teaching a switching circuit is provided. The method includes presenting a target within a sensing range of a sensor of the switching circuit for a pre-determined duration and acquiring an identification code of the target via the sensor. The method also includes storing the acquired identification code for operating the switching circuit and locking the switching circuit against learning identification codes of any other target prior to reaching an allowed number of reteaching attempts.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/610,793, entitled “Reteachable Switching Circuit with Ability forLocking,” filed Nov. 2, 2009, which is herein incorporated by reference.

BACKGROUND

The invention relates generally to switching devices, such as formachine guarding in industrial applications, and particularly toreteachable switching circuits with an ability for locking

Certain switching devices are known and are in use for controllingdevices in technical installations in a manner to prevent human accessto machines, such as presses and so forth. Typically, such switchingdevices are configured to facilitate partial or complete shutdown ofelectrically driven machines/devices of the technical installation toavoid or reduce the opportunities of access to equipment whenoperational.

One typical application of such a switching device is a door switch thatincludes an actuator-sensor combination for detecting an open state ofan access door of the technical installation (e.g., a press). Typically,the actuator is coded with a unique identification code that is utilizedby the sensor to detect the open state of the access door. In general,it is desirable to provide switching devices that can be retaught newactuators. However, certain users of such devices require the switchingdevices to be locked against reteaching of new actuators.

Certain manufacturers provide separate switching devices havingdifferent catalogue numbers for re-programmable and non re-programmableswitches. However, this results in double inventory of the switchingdevices which may be expensive to maintain.

Accordingly, it would be desirable to provide a switching device thatcan be retaught new actuators, while providing the flexibility oflocking the device against reteaching of new targets.

BRIEF DESCRIPTION

Briefly, according to one embodiment of the present invention, a methodfor teaching a switching circuit is provided. The method includespresenting a target within a sensing range of a sensor of the switchingcircuit for a pre-determined duration and acquiring an identificationcode of the target via the sensor. The method also includes storing theacquired identification code for operating the switching circuit andlocking the switching circuit against learning identification codes ofany other target prior to reaching an allowed number of reteachingattempts.

In accordance with another aspect, a method for teaching a switchingcircuit is provided. The method includes presenting a target within asensing range of a sensor of the switching circuit for a pre-determinedduration, acquiring an identification code of the target via the sensorand storing the acquired identification code for operating the switchingcircuit. The method also includes moving the target outside the sensingrange of the sensor and re-presenting the target within the sensingrange of the sensor within a pre-determined period to lock the switchingcircuit against learning identification codes of any other target priorto reaching an allowed number of reteaching attempts.

In accordance with another aspect, a reteachable switching circuit isprovided. The reteachable switching circuit includes a non-contactsensor and a target movable into and out of a sensing range of thesensor. The reteachable switching circuit also includes a processorconfigured to reteach the switching circuit for operation of theswitching circuit based upon an identification code of the target and tolock the switching circuit against further reteaching based upon otheridentification codes of any other targets prior to reaching an allowednumber of reteaching attempts.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a technical installation such as an electricalmachine within a controlled access environment in accordance withaspects of the present invention;

FIG. 2 illustrates another exemplary embodiment of an installation ofFIG. 1 in accordance with aspects of the present invention;

FIG. 3 illustrates another exemplary embodiment of the installation ofFIG. 1 in accordance with aspects of the present invention;

FIG. 4 illustrates an exemplary configuration of the switching circuitsemployed in the installations of FIGS. 1, 2 and 3, respectively, inaccordance with aspects of the present invention;

FIG. 5 illustrates an exemplary process of reteaching the switchingcircuits of FIG. 4 in accordance with aspects of the present invention;

FIG. 6 illustrates an exemplary process of locking the switchingcircuits of FIG. 4 against learning of identification codes of newtargets in accordance with aspects of the present invention; and

FIG. 7 illustrates exemplary process steps of identifying a valid targetfor reteaching the switching circuit of FIG. 4 in accordance withaspects of the present invention.

DETAILED DESCRIPTION

As discussed in detail below, embodiments of the present techniquefunction to provide a method for reteaching a switching circuit such asnon-contact switching circuits employed for machine guarding inindustrial applications. In particular, the present technique provides aswitching circuit that can be re-taught for a new target without anyoperator manipulation of the switching circuit. Further, the presenttechnique also provides a locking mechanism for the switching circuitthat enables locking of the switching circuit against learning a newtarget prior to reaching an allowed number of reteaching attempts.

References in the specification to “one embodiment”, “an embodiment”,“an exemplary embodiment”, indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Turning now to drawings and referring first to FIG. 1, a technicalinstallation such as an electrical machine 10 within a controlled accessenvironment 12 is illustrated. The machine 10 includes a power supply 14to power a plurality of switching circuits 16, 18 and 20 disposed onaccess doors 22, 24 and 26 respectively of the installation. In theillustrated embodiment, the power supply 14 includes a 24 volts DC powersupply. The switching circuits 16, 18 and 20 are configured to monitorposition of each of the access doors 22, 24 and 26 and to interruptoperation of the installation completely or partially to preventuncontrolled access to the installation when the doors 22, 24 and 26 areopen.

In the illustrated embodiment, each of the switching circuits 16, 18 and20 includes a non-contact sensor disposed on a stationary component suchas a frame of each of the access doors 22, 24 and 26 and a target suchas an actuator disposed on a movable component such as on surface ofeach of the access doors 22, 24 and 26. In a closed state of the accessdoors 22, 24 and 26, the actuator is located within the sensing range ofthe sensor, which causes an enable signal to be generated.Alternatively, in an open state of any of the access doors 22, 24 and26, the actuator is removed from the sensing range of the sensor, whichgenerates a switching signal for interrupting operation of one or morecomponents of the installation completely or partially through one ormore devices, such as represented by reference numeral 28.

In certain embodiments, the machine 10 includes output signal switchingdevices (OSSDs) that are configured to switch DC powered devices, suchas contactors and control relays of the installation. In one exemplaryembodiment, the OSSDs include PNP type transistors with short circuitprotection, overload protection and crossfault detection.

In this exemplary embodiment, the switching circuits 16, 18 and 20utilize radio frequency identification for coding of the actuator andinduction for sensing by the sensor. The teaching of such switchingcircuits 16, 18 and 20 will be described in detail below with referenceto FIGS. 4-6. In certain embodiments, the devices 28 include machineactuators or logic devices such as monitoring relays configured tointerrupt one or more components of the installation. The monitoringrelays may include two or more guided relays with additional circuitryto ensure performance of the access limiting function.

FIG. 2 illustrates another exemplary embodiment 40 of an installation 10of FIG. 1. As illustrated, the installation 40 includes switchingcircuits 16, 18 and 20 for monitoring a position of each of the accessdoors 22, 24 and 26. In this embodiment, the installation 10 includes acontroller 42 configured to receive switching signals from the switchingdevices 16, 18 and 20 and to generate output signals for the devices 28.In certain embodiments, the controller 42 includes a programmable logiccontroller (PLC) with solid-state outputs. In operation, the devices 28may be operated by the controller 42 in response to signals from theswitching circuits 16, 18 and 20. Thus, the devices 28 may shut down orinterrupt operation of certain devices of the installation 40 if theswitching circuits 16, 18 and 20 detect any of the access doors 22, 24and 26 in an open state.

FIG. 3 illustrates another exemplary embodiment 50 of the installation10 of FIG. 1. In this embodiment, the installation 50 includes a network52 to receive switching signals from the switching circuits 16, 18 and20 and to control operation of the devices 28. In certain embodiments,the installation 50 includes a remote controller 54 communicativelycoupled to the network 52 to analyze the switching signals and tocontrol the operation of the devices 28 to shut down or interruptoperation of certain equipment of the installation 50 based upon suchswitching signals. As will be appreciated by one skilled in the art thenetwork 52 may include components such as network cables, networkinterface cards, routers and bridges to communicate with the devices 28and the controller 54.

As described above, each of the switching circuits 16, 18 and 20includes the sensor and the target that has a unique identificationcode. Each of the switching circuits 16, 18 and 20 is configured to beretaught a new target without operator manipulation of the switchingcircuits 16, 18 and 20. Furthermore, an operator can lock each of theswitching circuits 16, 18 and 20 against further reteaching of any othertargets as will be described below.

FIG. 4 illustrates an exemplary configuration 60 of the switchingcircuits 16, 18 and 20 employed in the installations 10, 40 and 50 ofFIGS. 1, 2 and 3 respectively. Each of the switching circuits 16, 18 and20 includes a non-contact sensor 62 and a target 64 movable into and outof a sensing range of the sensor 62. In one embodiment, the sensingrange of the sensor 62 is between about 10 mm and about 25 mm. In theillustrated embodiment, the sensor 62 is disposed on a stationarycomponent such as frame of the access door 22 (see FIG. 1). Further, thetarget 64 includes an actuator disposed on a movable component such asthe access door 22.

The actuator 64 is coded with an identification code using radiofrequency identification. In one exemplary embodiment, theidentification code includes a 16-bit word. In operation, the sensor 62generates a radio frequency field, generally represented by referencenumeral 66, at frequency of about 125 kHz and the target 64 is a passiveresonant circuit that responds to excitation by the radio frequencyfield. Moreover, each of the switching circuits 16, 18 and 20 includescomponents 68 for reteaching the switching circuits 16, 18 and 20.

In particular, each of the switching circuits 16, 18 and 20 includes amemory 70 configured to store a plurality of identification codes ofother targets previously used by the switching circuits 16, 18 and 20respectively as a basis for switching. The memory 70 may include harddisk drives, optical drives, tape drives, random access memory (RAM),read-only memory (ROM), programmable read-only memory (PROM), redundantarrays of independent disks (RAID), flash memory, magneto-opticalmemory, holographic memory, bubble memory, magnetic drum, memory stick,Mylar® tape, smartdisk, thin film memory, zip drive, and so forth.

Further, each of the switching circuits 16, 18 and 20 includes aprocessor 72 configured to reteach the switching circuits 16, 18 and 20for the target if an acquired identification of the target is differentfrom all stored identification codes previously used by the switchingcircuits 16, 18 and 20 respectively as a basis for switching. Inaddition, each of the switching circuits 16, 18 and 20 includes adisplay 74 to display warning messages if the identification code of thetarget is identical to any stored identification code previously used bythe switching circuits 16, 18 and 20 respectively as the basis forswitching.

It should be noted that the present invention is not limited to anyparticular processor for performing the processing tasks of theinvention. The term “processor,” as that term is used herein, isintended to denote any machine capable of performing the calculations,or computations, necessary to perform the tasks of the invention. Theterm “processor” is intended to denote any machine that is capable ofaccepting a structured input and of processing the input in accordancewith prescribed rules to produce an output. It should also be noted thatthe phrase “configured to” as used herein means that the processor isequipped with a combination of hardware and software for performing thetasks of the invention, as will be understood by those skilled in theart.

In certain embodiments, each of the switching circuits 16, 18 and 20 mayinclude a buffer memory (not shown) configured to store sensing datacorresponding to the target 64 within a pre-determined duration tovalidate the acquired identification code of the target 64. In oneexemplary embodiment, the pre-determined duration is about 15 secs. Itshould be noted that the processor 72 is configured to reprogram theswitching circuit such as 16 without operator manipulation of theswitching circuit 16. Advantageously, the reteaching of the switchingcircuits 16, 18 and 20 can be performed without power cycling andwithout any manipulation of jumper connections of the switching circuits16, 18 and 20.

In certain embodiments, the processor 72 is configured to reprogram theswitching circuit such as 16 based upon the identification code of thetarget and to lock the switching circuit 16 against further reteachingbased upon other identification codes of any other targets prior toreaching an allowed number of reteaching attempts. In one exemplaryembodiment, the allowed number of reteaching attempts is 8. However, agreater or lesser number may be assigned for the allowed number ofreteaching attempts. It should be noted that an operator of the systemmay lock the switching circuit 16 either immediately after commissioningor after any subsequent successful learn of the switching circuit 16 fora target 64.

In operation, the target 64 is presented within the sensing range of thesensor 62 for a pre-determined duration and the identification code ofthe target 64 is acquired via the sensor 62. In this exemplaryembodiment, the pre-determined duration is about 15 seconds. Further,the acquired identification code is stored in the memory 70. Theswitching circuit 16 may be subsequently locked against learningidentification codes of any other target prior to reaching the allowednumber of reteaching attempts.

In this exemplary embodiment, each of the switching circuits 16, 18 and20 includes one or more light emitting diodes (LEDs), such asrepresented by reference numeral 76 for identifying location of faultsin the installation 10. For example, a green light emitted by the LED 76of the switching circuit 16 indicates that the target 64 is within thesensing range of the sensor 62 and the switching circuit 16 isfunctioning properly. Similarly, a flashing red light emitted by the LED76 of the switching circuit 18 indicates that the switching circuit 18has a fault and is not functioning properly. Further, a red lightemitted by the LED 76 of the switching circuit 20 indicates that thetarget 64 is outside the sensing range of sensor 62. Thus, based uponindications from the LED 76 of the various switching circuits 16, 18 and20 any faults within the installation 10 may be detected and corrected.

FIG. 5 illustrates an exemplary process 90 of reteaching the switchingcircuits 16, 18 and 20 of FIG. 4. At block 92, the process is initiatedand the power is supplied to the switching circuit. Further, a target ispresented within the sensing range of the sensor of the switchingcircuit. At block 94, the presence of the new target is detected and asolid red light is displayed by the LED of the switching device toindicate the absence of a learned target. In the illustrated embodiment,the target is presented in the sensing range for a pre-determinedduration. In one exemplary embodiment, the pre-determined duration isabout 15 secs. At block 98, it is validated if the target is present forthe pre-determined duration.

Further, it is verified if the target is an acceptable actuator for theswitching circuit (block 100). If the target is not an acceptableactuator then the switching device displays an error code using the LEDof the switching device, as represented by block 102. In this exemplaryembodiment, power cycling of the switching device is required for theswitching device for an unacceptable target, as represented by block104.

Alternatively, once an acceptable target is detected, then the switchingdevice proceeds with reteaching of the switching device for the targetby acquiring the identification code of the target via the sensor. Atblock 106, a timed loop with a pre-determined duration is initiated. Inthis exemplary embodiment, the timed loop has duration of about 15seconds. During the timed loop, green and red light may be displayedalternately by the LED of the switching device (block 108). The timedloop is completed after the pre-determined duration, as represented byblock 110. At block 112, the switching device validates if the targetwas present continuously during the timed loop. If the target was notpresent within the sensing range of the sensor for the entire durationof the timed loop, then an error code is displayed by the switchingdevice (block 114).

At block 116, the sensed data during the timed loop is compared tovalidate the acquired identification code of the target and powercycling of the switching device is performed if the acquired code isinvalid (block 104). In this exemplary embodiment, the identificationcode of the target is repeatedly sensed within the timed loop and iscompared to validate the acquired code. At block 118, the switchingdevice verifies if the current reteaching attempt is less than anallowed number of reteaching attempts. If the current reteaching attemptis greater than the allowed number of reteaching attempts, then an errorcode sequence is initiated, requiring power cycling.

Once the acquired identification code of the target is validated, it iscompared with all stored identification codes of other targetspreviously used by the switching circuit as a basis for switching.Further, the switching circuit is retaught based on the acquiredidentification code only if the acquired code is different from allstored identification codes of other targets previously used by theswitching circuit as a basis for switching. The acquired identificationcode is then stored for operating the switching circuit.

Further, the switching circuit may be locked against learningidentification codes of any other target prior to reaching an allowednumber of reteaching attempts, as illustrated by exemplary process 120of FIG. 6. At block 122, a timed loop for a pre-determined period for avalid target is initiated. In this exemplary embodiment, duration of thepre-determined period is about 15 secs. At block 124, number ofavailable reteaching attempts is displayed by the LED of the switchingdevice. Further, it is verified if the target is moved outside thesensing range of the sensor and is represented within the sensing rangewithin the pre-determined period (block 126).

In this exemplary embodiment, opening and closing of a movable componentsuch as an access door where the target is mounted is monitored toverify if the target is moved outside and is re-presented within thesensing range. In one exemplary embodiment, if the opening and closingof the movable component is performed at least once during thepre-determined period, then the locking of the switching device isinitiated. At block 128, the timed loop is ended and a green light isdisplayed by the LED of the switching device to indicate the completionof the timed loop (block 130). At block 132, the switching device islocked against learning identification codes of any other target.Further, the switching device is operated with the acquiredidentification code of the target (block 134).

If the opening and closing of the movable component is not performed atleast once during the pre-determined period and the timed loop iscompleted, as represented by blocks 136 and 138, then the learningability of the switching device is in the unlocked state (block 140).Thus, the switching device is open for learning identification codes ofother target presented within the sensing range of the sensor of theswitching device. Again, the switching device is operated with theacquired identification code of the target (block 142).

FIG. 7 illustrates exemplary process steps 150 of identifying a validtarget for reteaching the switching circuit 16 of FIG. 4. At block 152,the identification code of the target is acquired using the sensor ofthe switching device. In this exemplary embodiment, the identificationcode includes a 16-bit word. In this embodiment, the sensor generates aradio frequency field at a frequency of about 125 kHz and the target isa passive resonant circuit that responds to the excitation by the radiofrequency field. At block 154, the acquired identification code iscompared with currently learned stored identification code used by theswitching circuit as a basis for switching. If the acquiredidentification code is identical to the currently stored code, then anew code is not learnt and the switch continues normal operation.

If the acquired identification code is different from the currentlystored identification code used by the switching circuit as a basis forswitching, then it is verified if the state change counter of theswitching device is equal to zero (block 156). The state change counterserves as a filter to ensure that not every new identification code isvalidated by the process. The state change counter is incremented if areading matches the previous. If three readings in a row match, thevalidation process is triggered. If the state change counter is equal tozero, then a buffer is set equal to the current data and the statechange counter is incremented (blocks 158 and 160). The sensor thenacquires the next data reading.

Alternately, if the state change counter is not equal to zero, then itis verified if the current sensed data is equal to the buffer (block162). If the current sensed data is not equal to the buffer, then thebuffer and the counters are initialized, as represented by block 164.The sensor then acquires the next reading of the target.

If the current sensed data is equal to the buffer, then the state changecounter is incremented and it is verified if the state change counter isequal to three (blocks 166 and 168). The state change counter serves asa filter to ensure that not every new identification code is validatedby the process. The state change counter is incremented if a readingmatches the previous. If three readings in a row match, the validationprocess is triggered. If the state change counter is not equal to three,then the sensor proceeds to acquire the next reading corresponding tothe target in the sensing range of the sensor.

Alternately, if the state change counter is equal to three, then a timerloop of pre-determined period is initiated (block 170). In one exemplaryembodiment, the pre-determined period of the timer loop is about 15seconds. At block 172, if the current sensed data is equal to the tempbuffer, then the data counter is incremented before the timer loop iscompleted, as represented by block 174.

At block 176, it is verified if the data counter is greater than orequal to a pre-determined threshold. In this embodiment, thepre-determined threshold is about 90%. If the data counter is less thanthe pre-determined threshold, then the output is set for no targetpresent in the sensing range of the sensor (block 178). Subsequently,all buffers and counters are initialized, as represented by block 180.Alternatively, if the data counter is greater than or equal to thepre-determined threshold, then the sensed data is stored in the memoryand the output is set for target present in the sensing range of thesensor (block 184). Again, all buffers and counters are initialized, asrepresented by block 180. Thus, once a valid target is detected, theswitching circuit may be reprogrammed for the corresponding target andthe identification code of the target is stored for operation of theswitching circuit.

As will be appreciated by those of ordinary skill in the art, theforegoing example, demonstrations, and process steps may be implementedby suitable code on a processor-based system, such as a general-purposeor special-purpose computer. It should also be noted that differentimplementations of the present technique may perform some or all of thesteps described herein in different orders or substantiallyconcurrently, that is, in parallel. Furthermore, the functions may beimplemented in a variety of programming languages, such as C++ or JAVA.Such code, as will be appreciated by those of ordinary skill in the art,may be stored or adapted for storage on one or more tangible, machinereadable media, such as on memory chips, local or remote hard disks,optical disks (that is, CD's or DVD's), or other media, which may beaccessed by a processor-based system to execute the stored code. Notethat the tangible media may comprise paper or another suitable mediumupon which the instructions are printed. For instance, the instructionscan be electronically captured via optical scanning of the paper orother medium, then compiled, interpreted or otherwise processed in asuitable manner if necessary, and then stored in a computer memory

The various aspects of the structures described hereinabove may be usedfor reteaching switching circuits for various machines. In theinstallations discussed above, the present techniques would be used tolimit access to a workspace, machine, or the like. Many otherapplications exist, however, for verifying position of a movablecomponent with respect to a stationary component (or the position of twomovable components with respect to one another) that may be the subjectof application of the presently claimed techniques. In particular, thetechnique may be employed for machines where multiple access doors arerequired to be monitored employed in industries such as materialhandling, packaging, life sciences and fiber and textiles, to name justa few. As described above, the technique utilizes a reteaching methodfor training the switching circuit for a target without operatormanipulation of the switching circuit. Thus, any machine with a damagedtarget can resume working with new targets in relatively lesser timewithout requiring complex or disruptive steps such as cycling power etc.

The technique described above also provides locking of the switchingcircuit against learning of codes of new targets prior to reaching anallowed number of reteaching attempts. Advantageously, the techniquefacilitates reteaching of the switching circuit for a new target in anevent where the target has been damaged in the field while preventingby-passing of the switch by using any spare targets taped to the face ofthe switch by the operator/maintenance personnel thereby providing arobust and secure switching device.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

The invention claimed is:
 1. A method for teaching a switching circuit,comprising: acquiring an identification code of a target via a sensorwhen the target is presented within a sensing range of the sensor for apre-determined duration; storing the acquired identification code foroperating the switching circuit; and locking the switching circuitagainst learning identification codes of any other target, whereinlocking the switching circuit against learning comprises moving thetarget outside the sensing range of the sensor and re-presenting thetarget within the sensing range of the sensor within a pre-determinedperiod.
 2. The method of claim 1, wherein the sensor is disposed on astationary component and the target comprises an actuator disposed on amovable component within the sensing range of the sensor.
 3. The methodof claim 1, wherein the pre-determined duration is about 15 seconds. 4.The method of claim 1, comprising detecting the target within thesensing range of the sensor through radio-frequency identification. 5.The method of claim 1, wherein the moving and re-presenting steps areperformed at least once within the pre-determined period.
 6. The methodof claim 1, wherein the pre-determined period is about 15 seconds. 7.The method of claim 1, further comprising operating the switchingcircuit with the acquired identification code of the target presented.8. The method of claim 2, wherein moving the target comprises openingthe movable component to move the target outside the sensing range ofthe sensor and re-presenting the target comprises closing the movablecomponent to re-present the target within the sensing range of thesensor.
 9. The method of claim 8, wherein the opening and closing stepsare performed at least once within the pre-determined period.
 10. Areteachable switching circuit, comprising: a non-contact sensorconfigured to be disposed on a frame of an access door configured toprovide access to at least one electrically driven device for anindustrial application, the sensor having a sensing range; a targetconfigured to be disposed on the access door, wherein the target islocated within the sensing range of the sensor when the access door isclosed, and the target is located outside of the sensing range of thesensor when the access door is open; and a processor configured toreprogram the switching circuit for operation of the switching circuitbased upon an identification code of the target sensed by the sensor andto prevent the switching circuit from learning any other identificationcode of any other target sensed by the sensor, wherein the processor isconfigured to prevent the switching circuit from learning any otheridentification code when the target moves outside the sensing range ofthe sensor and is re-presented the target within the sensing rangewithin a pre-determined period.
 11. The reteachable switching circuit ofclaim 10, further comprising a memory configured to store theidentification code of the target.
 12. The reteachable switching circuitof claim 10, wherein the sensor generates a radio frequency field atapproximately 125 kHz, and the target is a passive resonant circuit thatresponds to excitation by the radio frequency field.
 13. The reteachableswitching circuit of claim 10, wherein the identification code of thetarget comprises a 16 bit word.
 14. The reteachable switching circuit ofclaim 10, wherein the identification code of the target is sensed withinabout 15 seconds.
 15. The reteachable switching circuit of claim 10,further comprising one or more light emitting diodes configured toindicate a status of the switching circuit, the sensor, the target, orany combination thereof.
 16. The reteachable switching circuit of claim15, wherein the status is indicated by: illuminating a first lightemitting diode of the one or more light emitting diodes; oscillating anillumination of the first light emitting diode; illuminating a secondlight emitting diode of the one or more light emitting diodes; or anycombination of the above.
 17. The reteachable switching circuit of claim16 wherein illuminating the first light emitting diode of the one ormore light emitting diodes corresponds to the target being within thesensing range of the sensor, wherein oscillating the illumination of thefirst light emitting diode corresponds to the target being outside ofthe sensing range of the sensor, and wherein illuminating the secondlight emitting diode of the one or more light emitting diodescorresponds to the switching circuit not functioning properly.